Any scam call I get usually I dont answer but if I do I let them say their spiel and then I scream as loud as I can in to their ear. Scares my family at first and then we all crack up. A whistle works great as well.
Scammers rotate numbers to try to catch you unaware, especially if you just erased it last time.
A tip: if your phone provider will only block a limited number of calls without charging you, consider buying a phone which has blocking features within the phone itself so you can block additional numbers -- they are fairly inexpensive and can be purchased anywhere.
My phone provider allows 30 (about a months worth for me). I am able to describe the call and I do so my dating it first, then describe the call, in this case medicare scam. When I reach 30 I delete the oldest one since by then they have changed phone numbers anyway.